Electronic control system for directing a torpedo at a target



D. B. HARRIS 3,196,82

ELECTRONIC CONTROL SYSTEM FOR DIRECTING A TORPEDO AT A TARGET July 27, 1965 4 Sheets-Sheet 1 Original Filed June 21, 1945 mw.. Wm,

JWM/KM y 27, 1965 D. B. HARRIS 3,196,321

ELECTRONIC CONTROL SYSTEM FOR DIRECTING A TORPEDO AT A TARGET Original Filed June 2l, 1945 4 Sheets-Sheet 2 www u* ww@ QN Y NNW N w xk mw mms @N wm `Fuly 27, 1965 D. B. HARRIS 3,96,2

ELECTRONIC CONTROL SYSTEM FOR DIRECTING A TORPEDO AT A TARGET Original Filed June 2 1, 1943 4 Sheets-Sheet 3 f77/venan M/W @FVW United States Patent O 3,196,821 ELECTRONTC CONTROL SYSTEM FOR DIRECTNG A TORPEDO AT A TARGET Donald B. Harris, Los Altos, Calif.; Leon A. Cai-ley, executor of said Donald E. Harris, deceased Continuation of application Ser. No. 491,616, .lune 21, 1943. This application Mar. 21, 1963, Ser. No. 267,397 Claims. (Cl. 114-23) The present application is a continuation of my patent application Serial No. 491,616 led lune 21, i943, now abandoned, and entitled Electronic Control System for Directing a Torpedo at a Target.

This invention relates to marine torpedoes, and more particularly relates to automatically controlled and directed marine torpedoes used in naval warfare to attack enemy vessels. It has particular application in use against enemy submarines, but may also be used against surface vessels.

Present methods of combating submarine attack depend principally on the use of depth charges dropped in the vicinity of the submarine by escort vessels. Results are unreliable, because the escort vessel is seldom in the vicinity of the submarine at the time when the submarines presence becomes known, either through its rising to the surface, or showing its periscope preparatory to firing its torpedoes. By the time the escort vessel reaches the approximate location where the submarine was seen, the submarine has submerged, and may already be some distance away. Depth charges dropped under these conditions may be relatively close to the submarine, but still not close enough to score a hit.

In accordance with the present invention, a soundcontrolled torpedo is provided, for use by the escort vessel in a manner similar to that now accorded depth bomb charges. A number of these torpedoes are carried by the escort vessel, which follows the present practice of reaching the approximate location where the submarine was last seen, as soon as possible after it has submerged. The escort vessel then lires a torpedo, which sends out a sound signal through the water. This sound signal, propagated in all directions except vertically from the torpedo, is reilected from the hull of the submarine back to the torpedo. A control system which is provided in the torpedo responds to this reected sound signal and actuates `a mechanism which at all times keeps the horizontal and vertical rudders of the torpedo so disposed that in its course the torpedo will remain pointed directly at the source of the reflected sound wave; or in other words at the submarine. The torpedo is, of course, equipped with the usual motors and propellers for propelling it forward, and with the usual explosive charges; it accordingly follows its course in the direction of the reilected sound wave until it meets the submarine and explodes.

Means are also provided in the invention for protecting the escort vessel, and preventing the torpedo from following a sound wave reflected from the hull of the escort vessel. These means consist principally of an apparatus for sending a second, neutralizing sound signal from the escort vessel, and appropriate means in the control system of the torpedo for recognizing this neutralizing signal and applying it to the directive mechanism of the torpedo in such a way as to neutralize the effect of `any reilection of the sound wave of the torpedo, from the hull of the escort vessel. The use of this neutralizing signal also has the eect of preventing the reflected sound wave from giving a false bearing to the torpedo, thereby causing it to follow an incorrect course not directed at the enemy submarine. An alternative method of preventing the effects of reflections from the escort vessel consists of directional means in the microphones of the torpedo 3,196,821 Patented July 27, 1965 ice which render them unresponsive to signals originating at any point above a certain depth in the water. The hull of the escort vessel may also be equipped with soundabsorbing material attenuating the reflection to a point where it will not act on the control system of the torpedo. A combination of these expedients may be employed. A time-delay relay is also provided which renders the control system inactive until, after the firing of the torpedo, it has traveled out of the sound range of the escort vessel and arrived in the vicinity of 'the target.

In carrying out this invention, I employ two independend control systems; one which actuates the vertical rudder of the torpedo, and one which actuates the horizontal rudder of the torpedo. lEach control system is provided with two microphone systems, rigidly attached to the torpedo, consisting of a non-directional microphone system, and a directional microphone system, the latter being so arranged that its response to signals coming from a certain direction is zero, or approximately zero. A sound signal is generated locally in the torpedo, by means of a high frequency oscillator and loudspeaker unit. This sound signal is intermittently interrupted by an interrupter. During the periods when the sound signal is being sent out, the microphone systems are disabled, so that they will not respond to sounds emitted directly by the loudspeaker. When the oscillator is interrupted by the interrupter, however, thereby stopping the emission of the sound signal, the microphone system is enabled by the interrupter. The reflected sound wave is received by the directional microphone which converts the sound wave to an electrical wave and impresses it on a modulator. A local tone signal generator, or low frequency oscillator, .separate and distinct from the oscillator and loudspeaker referred to above, is used to generate a signal also impressed on the modulator. Through the action of the modulator, the sound wave received by the directional microphone system is modulated by this signal. The modulated directional microphone signal is in turn combined with the signal from the non-directional microphone system, which also receives the reilected sound wave, and the result is introduced to an amplifier tuned to the frequency of the reflected sound wave. The output of this amplifier is impressed on a detector or demodulator, which derives from the complex wave a wave having a frequency equal to the frequency of the signal produced by the local tone signal generator in the torpedo and a phase relation dependent on the direction from which the reflected sound wave was received by the directional microphone system. This control wave is irnpressed on a system of thermionic tubes and relays arranged for reversioly operating a motor mechanically coupled with one of the rudders of the torpedo, either vertical or horizontal. This motor will operate either in a clockwise or counterclockwise direction, depending on the phase relation of the control wave, which, as detailed above, in turn depends on the direction from which the reflected sound wave was received.

The rudders or" the torpedo are accordingly moved in such directions that the torpedo tends to turn into line with the direction from which the reflected sound wave approached the torpedo. When the torpedo points exactly at the source of the reflected sound wave, the directional microphone Isystems cease to respond, and the level of the control waves fall below a predetermined amplitude, or to zero, bringing the motor drives to a stop, and holding the torpedo in a course directed at the target.

The neutralizing channels of the control systems consist of similar microphone, modulator, amplifier, detector and relay systems, tuned to the signal generated and sent out by the escort vessel. The output of the neutralizing amasar o: channel is, however, applied to oppose the output of the control or reflected channel, in the relay system. The level or amplitude of the neutralizing signal sent out by the escort vessel is exactly equal to the level received at the escort vessel from the signal sent out by the torpedo. Anyl reflection of the torpedos signal reflected back to the torpedo from the escort vessel will therefore be accompanied by a second signal of equal amplitude generated by the escort vessel, which, after transformation in the circuits of the neutralizing channel, will be applied to the control relay system in such a manner as to neutralize the effect of the wave reflected from the escort vessel.

The advantages of this sound-controlled torpedo over conventional methods of attack in warfare -against submarines will now be readily apparent. It is only necessary for the escort vessel to drop a torpedo in the general vicinity of the submarine whereupon the torpedo will automatically direct itself at the submarine, and will follow this course until the target has been reached. Moreover, any attempts of the submarine to evade the missile will be unsuccessful, as the torpedo automatically changes its course to follow any change in course made by the submarine. Quick dives made by the submarine will also be ineffective, as the torpedo is arranged to follow the target not only in azimuth, but also in depth. The necessity encountered under present systems, of gauging not only the location of the submarine in a horizontal plane, but also its depth, in order to set the depth charges properly is therefore obviated.

It is accordingly an object of my present invention to provide a marine torpedo which automatically directs itself at the target.

It is another object of my invention to provide a marine torpedo which directs itself automatically at the .target in response to a sound wave generated in the torpedo and reflected from the target.

A further object of the invention is to provide a torpedo which will automatically follow the target, while in motion, and will change its own course to match that of the target.

A further object of the invention is to provide a soundcontrolled, automatically directed marine torpedo equipped with a control system adapted to respond accurately to the reflected sound signals throughout a range of 360 degrees, without bi-directional ambiguity, and to keep the microphones of the system so disposed as to be operating at their null point throughout the course of the torpedo.

It is a further object of the invention to provide an automatically controlled marine torpedo equipped with a control system responsive to a signal reflected or transmitted from the target, and coupled to driving motors controlling the course of the torpedo in such a way as to keep the torpedo directed at the target.

A further object of the invention is to provide a marine torpedo equipped with a means for generating a sound signal propagated toward the target, and with means for responding to the refiection of this `sound signal from the target in order to direct the torpedo at the target, and with means for neutralizing any reflections of the same sound signal from the escort vessel, or other friendly vessels.

A further object of the invention is to provide a marine torpedo adapted to follow a signal reflected from the target, and to ignore reflections of the same signal from the hulls of friendly vessels.

A still further object is the provision of a sound-actuated direction indicating system applicable not only to torpedoes, but to other floating bodies or vessels to accurately point out through response to a sound signal proceeding from a target the direction of the target or other object.

The foregoing and other objects of my invention will be best understood from the following description of exemplifications thereof illustrated in the accompanying drawings, in which:

FIG. l is -a schematic mechanical and electrical block diagram of the components of the control system of my invention;

FIG. 2 is a schematic electrical circuit diagram of a control system embodying the principles of the present invention;

FIG. 3 is a schematic mechanical and electrical diagram, partially in block form, of the equipment provided in the escort vessel for sending out the neutralizing signal;

FIG. 4 contains graphs and diagrams illustrating the mathematical analysis of the control system treated under the heading Theoretical Consideration of the Control System. This figure includes the following sub-figures:

FIGURE 4A. Microphone input system.

FIGURE 4B. Wave front orientation.

FIGURE 4C. Graph of sound wave.

FlGURE 4D. Graph showing variation in maximum microphone voltage, ES, and of sin u, with rotation of sound wave front.

FIGURE 4E. Wave forms developed in the control system. Y

FlGURE 4F. Wave forms in the relay control tube system.

FIGURE l is an electrical block diagram illustrating the coaction of the components entering into the control system. Equipment for actuating either the vertical or the horizontal rudder is shown, together with the common equipment used for both horizontal and vertical rudders. The various classes of equipment are blocked loff from one another by dotted lines, and are identified as to their functions, the control channel for either horizontal or vertical rudder being shown at the bottom of the figure, the common equipment in the center, and the neutralizing channel for the corresponding rudder at the top.

Interrupter lf3 is of the multi-vibrator type, and is designed `to generate pulses at the rate of two to five cycles per second. These pulses, which consist of a momentary reduction of positive potential, are alternately applied to leads ll and 12. At the moment when a pulse is being applied to lead ll, 4the potential on lead l2 remains uniformly high, and vice versa. Leads 11 and l2 are connected to control the cathode bias of the microphone amplifiers in the control and neutralizing channels, and of the high frequency amplifier in the cornmon equipment channel, respectively. When the potential on these leads is high, rthe ampliers to which they are connected are disabled; when the potential is low the amplifiers are enabled. Thus, as the pulses are sent out by the interrupter, the amplifiers in the common equipment channel and in the control and neutralizing channels are alternately enabled, the control and neutralizing channels being disabled at any moment when the common equipment channel is enabled, and vice versa.

The tone emitted by the torpedo originates with high frequency oscillator f3. The frequency generated by this oscillator must be high enough to permit adequate waveinterference effects in the microphone and loudspeaker channels, and it is also desirable that it should be beyond the normal audible frequency range, in order to prevent discovery by the enemy of the method of operation of the control system; on the other hand, however, it cannot be too high without making the dimensions of the loudspeaker and microphone systems prohibitively small. In my system I prefer to use a frequency of approximately 15,000 cycles, but it is understood that other frequencies may be used.

Oscillator 13, then, continuously generates a frequency of 15,000 cycles during the period of operation of the torpedo, and this frequency is impressed on the input of high frequency voltage amplifier 14. When amplifier 1li receives a pulse over lead l2, it is enabled, and amplifies the 15,00() cycle signal, impressing it on the input of high frequency power amplifier 15. Amplifier l5 in turn amplies the signal and delivers it to loudspeakers 1.6 and 17.

Loudspeakers 16 and 17 therefore emit a pulse of the 15,000 cycle frequency, having a duration of from .10 second to .25 second, which travels outward through the water. The two loudspeakers are arranged vertically, one above the other, are operated in phase, and are spaced one-half wave-length apart. Under these conditions, sound waves propagated from the loudspeakers horizontally suffer no interference effects and are propagated with an amplitude equal to the sum of the amplitudes of the individual loudspeakers. Any sound wave propagated in a vertical direction from either speaker will, however, be exactly cancelled by the wave emitted vertically by the other speaker. This speaker system, therefore, propagates the 15,000 cycle signal outward horizontally from the torpedo, and also at an angle downward and upward, but it does not propagate the signal directly vertically upward, nor vertically downward. This feature is provided in order to avoid the effects of reflections of the sound wave either from the surface of the water or from the ocean bottom. Such reflections, if they existed, might turn the torpedo either vertically upward to the surface or vertically downward to the bottom, depending on the depth. Since the torpedo, however, emits no wave vertically upward or vertically downward, it is not affected by these reiiections.

Since the velocity of sound in sea water is approximately 1454 meters per second, the wave-length of the 15,000 cycle signal is (Mle-15,000) meters, or .09693 meter, or 9.693 centimeters. The loudspeakers are therefore spaced vertically 9.693 +2 centimeters, or 4.847 centimeters apart. The same effect can be obtained by disposing the loudspeakers horizontally one-half wave-length apart and operating them 180 degrees out of phase, and other configurations of phase and separation will also produce the same result. It is therefore understood that my choice of one-half wave length separation and zero phase difference is not to be construed as limiting my invention .to these requirements.

The duration of the pulse of 15,000 cycle signal, which is, of course, controlled by the frequency of the interrupter, is dependent on the maximum distance from the target at which it is desired to launch the torpedo or to enable the control system. If this distance be represented by s, the total distance traveled by the sound wave from .the torpedo to the target and back again will be 2s, and the time consumed in traveling this distance will be:

Where v is the velocity of the sound wave.

This time interval must be less than one complete period of the interrupter, because if it is greater than this value, the sound wave will arrive back at the torpedo at a moment when the microphone system is disabled. Or:

Where pis the period of the interrupter.

For example, if it is desired to launch the torpedo or to effect the enablement of the control system, `at a maximum distance of l200 meters from the target, the transmission time of the sound wave will be 40G/1454 seconds, or .275 seconds. The period of the interrupter must be greater than .275 seconds, and in this case would probably be chosen as .300 seconds, corresponding to a frequency of 3.333 cycles per second. As the duration of the 15,000 cycle pulse occupies one-half of the period of the interrupter, the `duration of this pulse will be `in this case .l5 seconds. Equation 2 shows that as the distance from the target becomes greater, the minimum period of the interrupter also becomes greater. It is, of course, not necessary to change the period or frequency of the interrupter each time the torpedo is launched. A period suitable for average battle conditions is selected, the interrupter is set at the corresponding frequency, and the torpedo is then launched within the range given by Equation 2 above or set so that the control system will start to function within this range.

When the sound wave emitted by the loudspeaker system traveling outward through the water, encounters the target, it is reiiected back to the torpedo. it is picked up by the microphones of the control channel. These microphones comprise, first a directional microphone system consisting of microphones A and B, and second, a nondirectional microphone, R. In the directional microphone system, microphones A and B are arranged on a line at right angles to the axis of length of the torpedo and are permanently attached to the body of the torpedo. in the case of the microphone system controlling the horizontal rudder of the torpedo (that is, the rudder which moves the torpedo about its vertical axis) the line joining the microphones is also horizontal, while for the microphones controlling the vertical rudder, the line is also vertical. In either case, microphones A and B are connected degrees out of phase: that is, a sound wave of given phase impressed simultaneously on A and B will produce an electrical wave in B which is 180 degrees out of phase with the electrical wave produced in A, and vice versa. Thus, any sound wave approaching the microphone system from a direction at right angles to the line joining microphones A and B will produce in each microphone a wave of similar amplitude but opposing phase, and when these waves are impressed together on the microphone input transformer, they will cancel one another, producing zero response in the grid circuit of the microphone amplifier.

Moreover, as will be shown later in connection with the theoretical treatment of the control system, any sound wave approaching the microphone system not from a direction at right angles to the line joining A and B, will roduce, in the two microphones, electrical waves which do not cancel one another when impressed on the microphone transformer, and therefore produce a resultant frequency in the microphone amplifier. A sound wave approaching to the right of the perpendicular to the line joining A and B produces a wave in the microphone transformer identical with the resultant produced by a sound wave approaching to the left of the perpendicular to the line joining A and B, except that the two waves are 180 degrees out of phase. For example, assuming that microphones A and R and B are spaced equi-distantly on the same line, `and assuming that microphone R receives a sound wave M cos 0, then the resultant in the microphone amplifier of A and B will be either N sin 0 or (-N sin 0), depending on Whether the sound wave approached from a direction to the left or to the right of the perpendicular to the line joining A and B. In other Words, a complete phase reversal takes place at the perpendicular.

As in the case of the loudspeaker system, other congurations of phase relationship and orientation will produce similiar results in the directional microphone system, and my choice of arranging the microphones at right angles to the axis of length of the torpedo, and connecting them 180 degrees out of phase is not `to be construed as limiting my invention to these requirements.

The spacing between microphones A and B depends on the frequency of the high frequency signal emitted by the torpedo. It will be shown later in connection with the theoretical treatment of the control system that maximum amplitude in the directional microphone system may be expected if the spacing is one-half wave length. With moderately high frequencies, however, this requirement results in a spacing so small that serious difiiculties are encountered in the mechanical construction of the microphone system. When .spacings .in excess of one-half wave length are used, secondary minima are encountered as the microphone system is rotated. However, as shown later, these secondary minima are not of serious consequence until the spacing reaches one full wave-length. I have accordingly selected, for practical application a spacing of .9 wave-length, between microphones A and B. Employing a 15,000 cycle signal, this value results in a spacing, between centers, of .9 9.693 centimeters, or 8.724 centimeters, providing dimensions in the system which are easily met by careful mechanical design. It is understood that further progress in the art may result in mechanical designs permitting closer spacing, and that accordingly my choice of .9 wave-length is not to be construed as limiting the spacing of the microphones to this figure. It should be noted, moreover, that a reduction in spacing may also be utilized to increase the frequency, leaving the spacing in terms of wave-length the same. if, for example, the spacing could be reduced to one-half the above figure, or to 4.362 centimeters, the frequency einployed could be increased to 30,000 cycles per second, maintaining the spacing, as referred to electrical units, at .9 wave-length. lt should be pointed out that the spacing in the neutralizing channel, though the same in terms of wave-length as in the control channel, will not be the same in terms of linear measurement, as the frequency differs in the two channels.

The resultant of the two waves picked up by microphones 1S(A) and 19(B) is impressed on microphone input transformer 20. This transformer is of a highly efficient type provided with a light iron core and especially designed to amplify the 15,000 cycle wave with a minimum of phase distortion. Condenser 21 in conjunction with the secondary winding of transformer provides an anti-resonant circuit tuned to 15,000 cycles. The voltage of the 15,000 cycle wave induced in the secondary winding is greatly enhanced by this anti-resonant circuit, and impressed on the input of high frequency microphone amplilier Z2. At the same time, the anti-resonant circuit tends to suppress waves of any other frequency which may enter the transformer, such as, for example the neutralizing signal from the escoit vessel, and to prevent the delivery of such frequencies to the microphone amplifier.

Amplier 22 ampliies the 15,000 cycle signal, and delivers it to modulator 23, where it is modulated by a low frequency signal derived from low frequency oscillator 24. This oscillator generates a frequency of approximately 100 cycles per second. The exact value of this frequency is not, however, critical, and other values may be used. Modulator 23 is of the balanced type, and the results of the modulation process is the creation of two side-band frequencies of 14,900 cycles and 15,100 cycles, respectively, the sum and difference of the 15,000 and 100 cycle frequencies. The original carrier frequency, 15,000 cycles per second, is not transmitted through the modulator. Viewed diagrammatically, the elfect of the modulation process is to create a modulation envelope of the carrier-suppressed type having a frequency of 100 cycles per second. An envelope of this type is shown in FlG. 4E(3). This modulation envelope is filled with oscillations of the 15,000 cycle wave, these oscillations having a phase identical with the phase of the resultant signal impressed on the microphone amplifier. This modulation process will be treated in more detail in connection with the theoretical consideration of the control system.

When the reflected sound signal reaches microphone 25(R), the reference microphone, it also creates an electrical signal, which is impredded by transformer 26 on high frequency microphone amplifier 2S after passing through the anti-resonant circuit provided by condenser 27 operating in conjunction with the secondary of transformer 26. After amplification by amplifier 28, the signal passes into phase network 29, which alters its phase by approximately 90 degrees. If, therefore the signal produced at the putput of reference microphone 25 was of the nature of (M cos 0) this same signal, after amplification and passage through the phase network will appear as (|-M sin 0). This correction of phase is necessary, because, as previously developed, if the reference microphone produces M cos 0 the directional microphone system will produce either (N sin 0) or N sin 0). As a result of the phase correction, the signal at the output of the phase network (-|M sin 0) has the same phase as, or a phase directly opposite to the signal at the output of the modulator (N sin 0 sin qb) or N sin 0 sin qs).

The modulated signal from the directional microphone system and the unmodulated signal from the non-directional microphone are now impressed simultaneously on detector 30 in such a manner that the voltages of the two signals are additive. The result of this process of addition is the creation of a modulation envelope of the percent modulation type, the outline of which is either approximately in phase with or approximately degrees out of phase with the original 100 cycle signal generated by oscillator 24, depending on whether the output of modulator 23 contained (N sin 9) or N sin 0); or in other words on whether the original sound signal approached the microphone system from the left or from the right of the perpendicular to the line joining the microphones. (See FlGURES 4E(5) and 4E(6).)

Detector 3d now rectilies this modulation envelope, reproducing the original 100 cycle wave generated by oscillater 24, either in phase with the original signal or 180 degrees out of phase With it, depending on the phase of the modulation envelope, and therefore in turn on the direction from which the sound wave approached the microphone system. The output of the detector is impressed on low frequency voltage amplifier 31, which arnplities the 100 cycle signal and delivers it to power amplilier 32. Amplifier 32 further ampliiies the signal and delivers it to the relay control tube system 33.

The original 100 cycle frequency generated by oscillator 24;- is also delivered to relay control tube system 33 after amplification by low frequency power amplifier 34. This relay control tube system is therefore subject to the effects of two 100 cycle signals, which are in phase if the original sound wave approached the microphone system from one side of the perpendicular to the line joining the microphones, and 180 degrees out of phase if the sound wave approached from the other side of the perpendicular. Control system 33 is so constituted that if these two signals are in phase the circuit to relay 35 will be completed, and this relay will operate, closing the circuit to motor 37, which will operate in a counterclockwise direction, rotating the rudder post and the rudder in a clockwise direction. If, however, the two signals `are 180 degrees out of phase, relay 36 operates, also closing the circuit to motor 37, but with opposite polarity. Motor 37 will then rotate in a clockwise direction, turning the rudder post and rudder in a counterclockwise direction. In either case, the rotation of the rudder will be in such a direction that the torpedo will be steered to turn into line with the direction from which the sound signal approached the torpedo. As the torpedo turns, the microphone system also turns, and when an orientation is reached such that the line joining the microphones is perpendicular to the direction of approach of the sound wave, the directional microphone system becomes unresponsive to the sound signal. The 100 cycle signal reaching the relay control tube system through the modulator channel then drops below a predetermined level, or to zero, the relay control tube system ceases to energize the relays, which return to normal, the motor is no longer energized, and ceases to rotate the rudder. Gear system 38 is coupled to the rudder through magnetic clutch 39. When the circuit to this clutch is opened, it uncouples the rudder from the gear assembly and motor, and the rudder returns to normal under the influence of spring 4l, which is held in post 42, attached to the framework of the torpedo. The torpedo will therefore continue its course along the line into which it has been turned, which is, `of course, directed to the source of the reflected sound wave, or in other words at the target. Any deviation of the torpedo from this course, caused either by a change in the direction of the torpedo or of the target, will cause the directional microphone system again to pick up the reflected signal and turn the torpedo into line again.

The high frequency signal generated by the torpedo, and emitted by the loudspeaker system, as it travels outward through the water, may also encounter the hull of the escort vessel, if the vessel is in the vicinity when the control system starts to operate. If this is the case, it will be rellected back to the torpedo and picked up by the microphone system, as in the case of the refiection from the target. This reflection from the escort vessel will pass through the control channel together with the reection from the target, and if allowed to actuate the relay control system would cause a false deviation in the course of the torpedo.

The escort vessel, however, is provided with means for picking up the signal emitted from the torpedo, and for emitting a similar signal on a different frequency, the amplitude of which is equal to that of the torpedos signal, as received at the escort vessel. These means are illustrated by FGURE 3 and will be described later. Any reflection from the escort vessel received by the torpedo will therefore be accompained by a neutralizing signal on a different frequency, having an amplitude equal to that of the reflection from the escort vessel. The frequency used for this signal is approximately 14,000 cycles, :although as in the case of the control channel, future improvements in mechanical design may permit the raising of this frequency.

This 14,000 cycle signal is picked up by the neutralizing channel of the control system and transmitted to the relay control system in a manner exactly similar to that employed by the control channel in handling the wave reliected from the target. The neutralizing channel is entirely similar in construction to the control channel except that it is tuned to 14,000 cycles, and the spacing of the microphones is altered to maintain a spacing of .9 wave-length with the 14,000 cycle frequency. Assuming a velocity of sound through sea water of 1454 meters per second, this requirement is met by spacing microphones A and B .9(1454+14,000) meters, or 9.3474 centimeters, apart, center to center, compared with the spacing of 8.724 centimeters employed for the control channel microphones. lt is necessary that the spacing in the control and neutralizing channels be the same in terms of wave-length, because, as will be demonstrated later in connection with the theoretical consideration of the control system, different spacings in the two channels would result in dis-similar responses to the reflected and neutralizing signals from the escort vessel, for certain orientations of the directional microphone systems.

The 14,000 cycle neutralizing signal is therefore picked up by the directional microphones, 43 (A) and 44 (B), in the neutralizing channel; amplified by high frequency microphone amplifier 47; modulated in modulator 48 by the same 100 cycle signal generated in oscillator 24 that actuates modulator 23; mixed, in detector 54 with the wave received by nondirectional microphone 49 (R), after its amplification in high frequency microphone amplifier 52, and its phase correction in phase network 53; and rectified by detector 54. The resultant 100 cycle signal is amplified by amplifiers S5 and 56, and impressed on relay control tube system 33. The signal entering the relay control tube system from amplifier 56 is similar in all respects, including amplitude, to the 100 cycle signal resulting from the reflection of the torpedos signal from the escort vessel, and impressed on the relay control tube system by amplifier 32, after transformation in the circuits of the control channel. The output circuits of amplifiers 56 and 32 are, however, connected 180 degrees out of phase. The neutralizing signal delivered by amplifier 56 therefore opposes the control signal in amplifier 32 developed from the refiection from the escort vessel, cancels it, and prevents it from actuating the relay control tube system.

The control channel, of course, is not responsive to the neutralizing signal, as it is tuned to the frequency of the signal emitted by the torpedo, 15,000 cycles per second, and suppresses the 14,000 cycle signal of the neutralizing system. Similarly, the neutralizing channel is not responsive to any refiections of the signal emitted by the torpedo, as it is tuned to 14,000 cycles, and suppresses the 15,000 cycle frequency.

FIGURE 2 is a schematic electricalj circuit diagram, illustrating electrical details of important features comprising a practical automatic torpedo control system constructed in accordance with the principles of my present invention. In this drawing, the detailed electrical connection of the various functional units of the control system, as shown in block form in FIGURE l, are delineated. ln each case the functional units retain the same identification and number as were used in FIG- URE l.

interrupter 10 is disclosed as a multi-vibrator circuit, in which extremely low frequency oscillations are generated through the medium of voltages fed back from the plate of triode tube to the grid of triode tube 101 through condenser 102, and from the plate of tube 101 to the grid of tube 100 through condenser 103. The mode of operation of multi-vibrator circuits is well known and will not be described in detail here. The frequency of the oscillations is controlled by the value of condensers 102 and 103 and of resistances 104 and 105.

The multi-vibrator interrupter 10, controls the operation of the sending and receiving channels 0f the control system in the following manner:

One characteristic of muti-vibrator circuits is that the two tubes alternately draw plate current, at a relatively steady value, and are suddenly forced to a cut-off condition, in which no plate current is drawn. Thus, while tube 100 is drawing plate current, tube 101 will be cutoff. This condition will exist, for the frequency previously set up, for about .l5 second. During this period, current flows from the B supply through resistance 107, the space current path in tube 100, and cathode resistor 112, to ground. The current fiow through resistor 107 causes a potential drop, so that the voltage at the junction between resistors 107 and 108 is less than the voltage of the B supply. The voltage at the junction between resistors 107 and 108 causes current to fiow through resistors 100 and 111 to ground, setting up a potential drop across resistor 111. This potential drop directly supplies the cathode bias of amplifier tubes 113, 114, and 116, in the microphone circuits of the control and neutralizing channels. With current flowing in tube 100 of the interrupter, the voltage set up across resistor 111 is of the correct value to enable tubes 113, 114, 115, and 116 to function as amplifiers, and the microphone systems are therefore enabled.

Also during the initial .15 second period, the grid bias of interrupter tube 101 due to the multi-vibrator action is maintained at a high negative value, to an extent that the tube is placed beyond cutoff, and no plate current flows. Under these conditions, the voltage on the plate of tube 101 is nearly equal to the voltage of the B supply, and this voltage causes an extremely high voltage to be set up across resistor 110. This voltage directly provides the cathode bias of tube 117 in the loudspeaker amplifier, and under these conditions the grid bias of tube 117 is placed beyond cutoff, disabling the loudspeaker amplifier, and preventing the emission of the loudspeaker signal.

At the expiration of the .15 second interval, tube 100 suddenly is placed beyond cut-off, through the multivibrator action, and ceases to draw plate current. The voltage at the junction between resistors 107 and 103 rises nearly to the voltage of the B supply, and similarly, the voltage across resistor 111 rises to a high value, raising the grid bias of tubes 113, 114, 115 and 116 beyond the cutoff point, and disabling the microphone systems.

Also at the expiration of the .15 second interval tube 101 suddenly starts to draw plate current, due to the multivibrator action. The voltage drop across resistor 106 lowers the voltage at the junction between resistors 105 and 109, the voltage drop across resistor 110 is also lowered, the grid bias of tube 117 is reduced within the operating range of the tube, and amplifier 14 is placed in condition to amplify signals from oscillator 13, and transmit them to the loudspeakers, through amplifier 15. The torpedo thereupon emits a signal which persists for approximately .15 second, until the multi-vibrator action suddenly causes tube 100 to start drawing current again, and tube 101 to cease drawing current, re-establishing the original condition. The cycle is then repeated, and continues to be repeated, as long as the interrupter continues to function.

Oscillator 13 is of the conventional feed-backtype, timed to 15,000 cycles by means of condenser 119, connected across the primary of transformer 120, which delivers the output of the oscillator tube 11S to tube 117 in the high frequency voltage amplifier 14.

Tube 117 is in turn coupled to power amplier 15 by transformer 121. Power amplifier 15 is of the push-pull type containing triode tubes 122 and 123. This type of amplifier is employed in order to permit emission of the purest possible tone signal, and at the highest possible level. Amplifier 15 is also tuned to the 15,000 cycle frequency in order to suppress undesirable harmonics. This tuning is accomplished by the resonant circuit provided by condenser 124, shunted across the secondary winding of transformer 121.

Loudspeakers 16 and 17 may be of the permanent magnet type, as shown, or may be of the type equipped with electrically energized iields. The output of power arnplier 15 is delivered to the loudspeakers through output transformer 125.

Microphones A, B and R may be of any type, crystal, dynamic, ribbon, etc. High frequency microphone ampliiers 2S and 2?, consist of pentode tubes 115 and 116 equipped with Volume control potentiometers 126 and 127. These potentiometers are employed to adjust the directional and non-directional signals to their proper relative values.

T he output of tube 116 in amplifier 22 (as shown in curve (l) of FIGURE 4E) is delivered to modulator Z3 by transformer 123, the secondary winding of which is tuned to 15,000 cycles by condenser 129. This second tuned circuit increases the selectivity of the control channel, and further suppresses any extraneous frequencies which may be picked up, including the neutralizing signal.

Modulator 23 is of the balanced type, consisting of triode tubes 130 and 131. The 15,000 cycle signal is impressed on the grids of the modulator tubes in parallel, through condensers 132 and 133. These condensers are of relatively small capacity, so that they exert a minimum of shunting effect on the low frequency signal also impressed on the modulator from oscillator 24. They are of sufficiently large capacity, however, to present a low reactance to the high 15,000 cycle signal delivered by the microphone system.

Tubes 130 and 131 in the modulator are maintained at a high normal grid bias by means of cathode resistor 1341, which interposes a high value of resistance in the plate current path, and which therefore maintains a high voltage between the cathode and the grid. This grid bias is sufciently high so that when the tubes are not excited, they operate close to the cut-ott point, and little plate current tlows. When the grids of tubes 130 and 131 are excited in phase by the 15,000 cycle signal, in the absence of any excitation from oscillator 24, successive half cycles of the exciting signal alternately raise the potentials of both grids simultaneously above the cut-off point and lower the potentials of both grids simultaneously below the cut-oit point. The potentials of the plates of the tubes similarly rise and fall together, in such a CFI manner that the potential on the two ends of the primary winding of transformer 135 is always equal, no current flows through the transformer, and the exciting signal is not transmitted to detector 30. If, however, the two grids are also excited 180 degrees out of phase by the 100 cycle signal derived from oscillator 24, as shown in FIG. 4E, (2), then during the half cycle of the 100 cycle signal which impress a positive voltage on tube 130, the bias of tube 130 is raised above the cut-off point, and the 15,000 cycle signal appears at the plate of the tube; while at the same time, the cycle signal impresses a negative voltage on the grid of tube 131, causing its bias to become even more negative, forcing the tube definitely beyond the cut-off point, and disabling it so that the 15,000 cycle signal does not appear at the plate of tube 131. Under these conditions, the 15,000 cycle signal in tube 130, not being opposed by a similar signal in tube 131, flows through the upper half of the primary of transformer 13S, to the B supply terminal. Due to the normal transformer action, a similar signal is generated in the secondary winding and impressed on the detector circuit 30.

Similarly, during the half cycles of the 100 cycle signal which impress a positive voltage on tube 131, the bias of tube 131 is raised above cut-oil?, permitting it to pass the signal through to the plate circuit, while at the same time tube is forced beyond cut-otf by negative voltage received by its grid from the 100 cycle signal, disabling the tube. The 15,000 cycle signal then liows from the lower terminal of transformer 135 through the primary winding to the B supply terminal, causing a similar signal to appear on the secondary winding.

Modulation of the carrier suppressed type is thus elfeetuated. The useful result of this process, as will be demonstrated mathematically later, is to multiply the amplitudes of the 15,000 cycle signal and the 100 cycle signal together, so that the output contains (N sin 0 sin p), where sin 0 represents the instantaneous value of the 15,000 cycle signal, and sin qs represents the instantaneous value of the 100 cycle signal. Thus the amplitudes of the 100 cycle signal directly controls the amplitude of the 15,000 cycle signal appearing in the output, which starts at zero amplitude, rises to maximum amplitude, and falls back to zero amplitude again during each half cycle of the 100 cycle signal as shown in curve (3) of FIGURE 4E. The 15,000 cycle oscillations retain their original phase characteristics inside the envelope, having one phase if the sound signal approached from one direction and a phase degrees removed if the sound signal approached from the other direction. The phase reverses in successive half cycles of the modulation envelope.

The modulated 15,000 signal is now delivered to detector 30 by transformer 135. In detector 30, the modulated directional signal is first mixed with the unmodulated non-directional signal derived from the non-directional microphone after it has been ampiilied by ampliiier 23. This amplifier consists of a resistance coupled pentode tube, 115. The output of amplifier 28 is delivered to detector 30 through phase network 29. This network consists of a series resonant circuit, including condenser 136 and inductance 137. This circuit is tuned to the 15,000 cycle signal, under which conditions, as is well known in resonant circuits, the reactance of the circuit drops to zero, and the combination of the condenser and inductance o'iers a purely resistive impedance to the ow of current. Under these conditions, the current through the network is in phase with the voltage appearing on the piate of tube 11S, the instantaneous value of which, as has been stated previously, is a linear function of (cos 6), since it is derived from the non-directional microphone. The current through the network after reversal of phase in the amplifier is therefore also a linear function of cos 0). As is well known, however, the current through an inductance lags behind the voltage across the inductance by an angle of 90 degrees. The

voltage across the inductance therefore leads the current by 90 degrees, and is a linear function of (-{-sin 0), as shown in curve (4) of FIGURE 4E. This voltage is delivered to detector 30 in series with the secondary of transformer 135, so that the voltage in the transformer is added to the voltage across inductance 137.

It will be observed that the modulated and unmodulated signals are now in phase, or 180 degrees out of phase, due to the phase correction made by the phase network. The result of adding them together is that during the half cycles of the modulation envelope when the modulated signal is in phase with the unmodulated signal, the two signals will reinforce one another, producing a maximum amplitude equal to the sum of their indivdual amplitudes; while during the half cycles of the modulation envelope when the modulated signal is 180 degrees out of phase with themodulated signal they will oppose one another, producing a minimum amplitude equal to the difference between their individual amplitudes. The modulation envelope therefore, instead of returning to an amplitude of zero every half cycle, now maintains a high value during one halt cycle, and a low value during the successive half cycle of the 100 cycle modulating signal. Whether the first half cycle is high and the second half cycle is low, or vice-versa depends on the phase of the 15,000 cycle oscillations and consequently on the direction from which the original sound signal approached the torpedo. -In one case, as shown in FIGURE 4E (5), the outline of the new modulation envelope, which is now of the 100 percent modulation type, will be in phase with the original 100 cycle tone generated by oscillator 24; in the other case, as shown in FIGURE 4E (6), the outline of the modulation envelope will be 180 degrees out of phase with the oscillator signal.

Detector 30 now rectifies the modulation envelope, reproducing an unmodulated 100 cycle frequency having a phase identical with the outlines of the modulation envelope, and therefore either in phase With the original oscillator 24 signal or 180 degrees out of phase with it depending on the direction from which the sound signal approached.

Detector 30 is of the conventional diode type. The secondary winding of transformer 135 is tuned to 15,000 cycles by means of condenser 138, in order to further suppress extraneous signals. The rectified signal delivered by diode detector tube 139 appears across resistance 140, which is shunted by condenser 141 in order to provide a path for the residue of the 15,000 cycle signal.

The 100 cycle signal appearing across resistance 140 is delivered to amplifier 31 through condensery 141a, and potentiometer 142, which is employed to adjust the level of the 100 cycle signal to match properly the 100 cycle signal delivered directly to therelay control tube system by oscillator 24. Amplifier 31 contains pentode tube 143, which is coupled to W frequency power amplifier 32 by means of resistance coupling, consisting of plate supply resistor 144, condenser 145 and grid resistor 146. Amplifier 32 contains triode tube 149, designed to develop power, and a phase correcting network consisting of resistor 147 and condenser 148. This phase correcting network performs the function of correcting any phase distortion which may have taken place in ampliers 31 and 32, in detector 30, or which may occur in the input circuit of the relay control tube system, in order to assure that the amplified 100 cycle signal from amplifier 32 will be in phase, or 180 degrees out of phase, in the relay control tube system, with the 100 cycle signal delivered to the relay control tube system directly by oscillator 24.

The output of amplifier 32 is coupled into relay control tube system 33 by transformer 150. Only one half of the primary winding of this transformer is used for the control channel, the other half being used by the neutralizing channel. The secondary of transformer 150 is tuned to 100 cycles by condenser 151. The 100 cycle signal is impressed in parallel on elements 152 and 153 of tubes 158 and 159 in the control system, through resistances 160 and 161, and in series with a positive bias derived from the B supply through resistors 162 and 163, with resistor 164 in shunt to ground. Resistor 246 is used to adjust the amplitude of the 100 cycle signal impressed on elements 152 and 153, and the relative values of resistors 162, 163 and 164 determine the value of the bias on these elements.

The 100 cycle signal from oscillator 24 is also impressed on elements 156 and 157 of tubes 158 and 159, after passing through low frequency amplifier 34. The signal from amplifier 34 is impressed on elements 156 and 157, 180 degrees out of phase, in series with the windings of relays 360 and 361, Which are shunted by condensers 362 and 363. The signal is delivered from amplifier 34 through transformer 364, which is of the stepdown type, and which is shunted by resistor 330 and condenser 331 to assure good voltage regulation under conditions when tubes 158 and 159 are drawing current. Amplifier 34 is a push pull amplifier equipped with beampower tubes 165 and 166, designed to give large power output. It is resistance-couilled from oscillator 24 by means of center-tapped resistor 167 and condensers 166 and 169. Oscillator 24 contains triode tubes 170 and 171, which produce oscillations by means of energy fed back from the plate of tube 170 to the grid of tube 171 through condenser 172 and from the plate of tube 171 to the grid of tube 170 through condenser 173. Grid resistors 174 and 175 are provided with taps, from which the 100 cycle signal voltage is fed to the control and neutralizing channels, through condensers 176 and 177. The oscillator is tuned by the resonant circuit consisting of condenser 178 and center-tapped inductance 179, which also serves as the plate supply feed for the oscillator tubes.

The B supply for the oscillator and the relay control tube system is maintained at a constant voltage, in order to improve the reliability and accuracy of the control system, by the interaction of condenser 180, resitsor 181, and voltage control tube 182. This tube is rated to maintain a voltage of 150 volts at point 133. An increase in the voltage supply to point 183 causes additional current to ow through tube 182, increasing the potential drop across resistor 181, and maintaining the voltage at point 183 constant in the well-known manner of Voltage regulators.

The relay control tube system 33 operates in the following manner:

Tubes 158 and 159 may be high vacuum triodes, mercury vapor relay tubes or thyratrons, or cold cathode glow-discharge tubes with a starter-anode. The tubes illustrated are the latter type, and are known currently as type 0A4G. They are designed so that a voltage of 110 volts at starter-anodes 152 and 153 will fire, or break down the tube affected and establish current fiow between anodes 156, 157 and cathodes 154, 155. The initial` positive bias on starter anodes 152 and 153 is of the order of 85 volts to ground. Cathodes 154 and 155 are normally maintained at a positive l2 volt potential with respect to ground, through cathode resistors 184 and 185 connected to battery through relay armatures `186 and 137. The relative potential of starter anodes 152 and 153 with respect to anodes 156 and 157, which are grounded, is 85 volts, and the relative potential of starter anodes 152 and 153 with respect to cathodes 154 and 155 is 85 minus 12, or 73 volts.

Transformer 364 continuously impresses a voltage of approximately l5() volts to ground on anodes 156 and 157, ias shown in curves (2) and (3) respectively of FIGURE 4F. This voltageis the alternating peak voltage of the signal derived from oscillator 24. Since it is impressed degrees out of phase on the two tubes, and since it is either in phase with or 180 out of phase with the control signal impressed in phase on starter anodes 152 and 153, as shown in curve (l) of FIGURE 4F, either starter anode 152 will be in phase with anode 156, or starter anode 153 will be in phase with anode 157. However, if the elements of tube 158 are in phase, the elements of tube 159 will be out of phase. By lin phase is meant that the two elements are positive with respect to ground at the same moment, and negative with respect to ground at the same moment.

When the control signal impressed on elements 152 and 153 reaches a value of approximately 30 volts, the total voltage of the starter anodes with respect to ground reaches 115 volts, placing both tubes in condition to fire. Only the tube however, in which the starter anode and the anode are in phase, will break down, because in the other tube the anode Will be negative at the moment when the starter anode is positive, and the a-node will therefore not be in -a condition to draw current, even through the starter anode has placed the tube in condition to fire.

Now, if the control signal derived from the control channel is in phase with the signal from the oscillator the circuit is so connected that tube 158 will have its elements in phase. Under these conditions, tube 158 will therefore fire as shown in curve (4) of FIGURE 4F. If, however, the two signals are 180 degrees out of phase, the elements of tube 159 will be in phase, and 'tube 159 Will fire, as shown in curve (5) of FIGURE 4F. The choice of the tube which fires is therefore dependent on the relative phase relationship of the two signals, and therefore on the direction from which the original sound signal approached the torpedo.

The firing of the tube continues only during the half cycle when both elements are positive. When both elements become negative on the succeeding half cycle the firing stops, to be resumed on the next positive half cycle. The control relay, however, pulls up and is energized during the positive half cycles, and the interval of time in the negative half cycles during which no current flows is too short to allow the relay to fall back. The relay therefore operates and remains operated as long as the tube continues to fire on the positive half cycles.

The operation of either of the two control relays causes current to flow, from battery on the movable spring of the unoperated relay, through the motor and electromagnetic clutch in parallel, to ground on the stationary spring of the operated relay. The direction of current flow, however, and consequently the direction of rotation of the motor, depends on which of the two control relays is operated, and therefore on the direction from which the original sound signal approached the torpedo. The field of the motor is, of course, continuously energized in one direction; a reversal of the direction of cur rent flow through the armature therefore causes the motor to reverse.

As stated in connection with FIGURE 1, the neutralizing channel response to the neutralizing signal sent out by the escort vessel in a manner exactly similar to the manner in which the control channel responds to the control signal. The features of the neutralizing channel are also identical with the features of the control channel, except that the neutralizing channel is tuned to a frequency of 14,000 cycles, while the control chan-nel is tuned to 15,000 cycles, and the separation of the microphones in the neutralizing channel is greater in linear measurement, than that in the control channel, in order to preserve the same separation in both channels in terms of wavelength. The electrical details of the neutralizing channel will therefore not be described, except to point out that the polarity of the connections of oscillator 24 to both the modulator in the control channel and the modulator in the neutralizing channel is identical. Therefore, a signal appearing in the neutralizing channel as a result of a neutralizing signal sent out by the escort vessel, after modulation will produce a 100 cycle wave in the detector circuit of the neutralizing channel in phase with the 100 cycle wave resulting in the detector circuit of the control Channel from a reflection of the control signal from the escort vessel. The connections at the output of the control channel and neutralizing channel however, are degrees out of phase, so that these two 100 cycle signals, still in phase after amplification in the respective low frequency amplifiers of the control and neutralizing channels, will oppose and cancel each other in winding of transformer 150, preventing any signal from the escort vessel from reaching the relay control system.

Relay 249 is a slow-acting relay, preferably of the solenoid type equipped with a piston and cylinder known as a dash-pot. The contacts of this relay are inserted in series with the motor circuit. When the torpedo is fired, relay 249 is momentarily energized, breaking the circuit, and disabling the control system. It returns to normal slowly, and finally closes the motor circuit after the torpedo, under the control of the conventional gyroscope, has passed out of the sound range of the escort vessel and into the vicinity of the target. This feature is provided as an additional safe-guard against possible false bearings due to the reflections from the escort vessels hull. lt may be employed optionally, land the relay may be set for any desired elapsed-time interval.

Equipment in the neutralizing channel includes, in addition to the microphone system already described:

Potentiometers 188 and 189, for adjusting the relative level of the directional and non-directional systems, respectively.

Coupling transformer 190, between the directional microphone amplifier and the modulator. The secondary of this transformer is tuned to 14,000 cycles by condenser 191.

Coupling condensers 192 and 193.

Modulator tubes 194 and 195, the bias of which is maintained by cathode resistor 196 and condenser 197.

Coupling transformer 198 between modulator 48 and detector 54. The secondary of this transformer is tuned to 14,000 cycles by condenser 199.

Condenser 200 and inductance 201, in phase network 53.

Detector tube 202, provided with load resistance 203, condenser 204, yand coupling condenser 205.

Low frequency voltage amplifier tube 207, provided with input potentiometer 206, and plate feed resistor 208.

Coupling condenser 209.

Low frequency power amplifier tube 213, provided with grid resistor 210, and a phase correcting network consisting of resistor 211 and condenser 212.

Miscellaneous equipment in both the control and neutralizing channels, not previously Idescribed specifically in connection with either FIGURE l or FIGURE 2, includes:

Cathode resistors, for maintaining proper bias conditions in various tubes, 214, 215, 216, 217, 218, 219, 244, 247.

Cathode condensers shunted across cathode resistors to provide a path for alternating currents in the cathode circuits, 220, 221, 222, 223, 224, 225, 226, 227, 228, 235, 245, 248.

Screen-grid supply resistors, in pentode tube circuits, 229, 230, 231, 232, 233, 234.

Voltage-divider resistors, inserted in the modulator input circuits for the purpose of adjusting the level of the modulating voltage, 236, 237, 238, 239, 240, 241, 242, 243.

Variable resistor 246, in the relay Acontrol tube system, used to adju-st the level of the incoming control signal, so that it will maintain the proper relationship to the level of the Vsignal derived directly from oscillator 24.

Microphones C and D, provided optionally in both channels, for the purpose of rendering the microphone systems insensitive to reflected signals coming from a point above a certain depth in the water. Microphone C would ordinarily be separated vertically from microphone A by one half-wave-length, and the two microvphones would be operated in phase, thereby providing a suppression of signals approaching vertically, and considerable attenuation of signals approaching from above or below, even if not vertically. This feature provides additional protection for the escort ve-ssel, which ordinarily is at a higher level than the target. Micro-phone D and B `are separated and 'operated in the same manner as C and A.

FIGURE 3 is a schematic mechanical and electrical diagram, partially in block form, of the equipment provided in the escort vessel, or other friendly vessel, for sending out the neutralizing signal. This equipment comprises two units: first, a neutralizing system, consisting of a set of modulators, an oscillator, and amplifiers for picking up the 15,000 cycle sound signal emitted by the torpedo, and converting it to ia 14,000 cycle neutralizing signal, the detailed connections of this equipment being shown in the lower half of the drawing; and second, a directional contro-l system similar to the control channel of FIGURE 1, provided for the purpose of indicating the direction from which the signal emitted by the torpedo comesJ and of adjusting the gain of the neutralizing system to compensate for variable coefficients of reflection from the .sides of the escort vessel. As the electrical circuits of this directional control system are identical in all respects with the control channel of `FIGURE 1, they are shown in block form only in the upper half of FIG URE. 3, and detailed connections are not indicated.

The directional control system is provided with two microphones, 250 (A) and 251 (B), forming a directional microphone system, rand a third microphone 252 (R) for reference purposes, just as in the case of the control system in the torpedo. These microphones are, however, mounted on a horizontal aXis which pivots around the the vertical shaft 301 of the motor system, and which is attached rigidly to this shaft. The view of the motor system shown is a plan view, looking down from above. Thus, when motor 253 operates, it causes the entire microphone system to rotate about a vertical axis, through the interaction of bevel gears 254 and 255, clutch 255 being operated whenever the motor is energized. The operation of the directional control system is entirely similar to the control channel in FGURE 1; that is, the motor causes the vertical .shaft to rotate whenever the front of the approaching sound wave is not parallel to the axis of the microphone systems. The reference microphone is, however, reversed in its connection to the control system, with respect to FIGURE l. A clockwise rotation of the sound-wave front therefore causes a clockwise rotation of the vertical shaft, and a counterclockwise rotation of the sound-wave front causes a counterclockwise rotation of the vertical shaft. Motor 253 therefore rotates the microphone syste-m in such a manner that its axis of length always remains parallel to the front of the approaching sound wave. A pointer 257 is attached to the vertical shaft at right angles to the axis of length of the microphone system; the pointer therefore always points directly at the torpedo, providing an indication of the whereabouts of the torpedo. Cam 25S and slider 259 also perform the function of adjusting the gain of the neutralizing system, by chan-ging the setting of potentiometer 260. The operation of this gain control will be described later in connection with the neutralizing system.

The directional control system comprises High Frequency Microphone Amplifiers 261 and 262, Modulator 263, Detector 264, Phase Network 2de', Low Frequency Amplifiers 266 yand 267, Relay Control Tube System 268, and Low Frequency Oscillator 2e9, corresponding, respectively, to High Frequency Microphone Amplifiers 22 and 28, Modulator 23, Detector 30, Phase Network 29, Low Frequency Amplifiers 31, `32 and 34, Relay Control System 33, and Low Frequency Oscillator 24, in FIG- URE 1. Transformers 270 and 271 are tuned to 15,000 cycles by means of condensers 272 and 273 connected across their secondary windings. Relays 274 and 275 l@ correspond to relays 35 yand 36 in FIGURE 1, land control the operation of Motor 253.

The neutralizing system comprises Modulator 274, High Frequency Oscillator 275, Dernodulator 276, Voltage Amplifier 277, Power Amplifier 278, and Loudspeaker 279. A portion of the 15,000 cycle sign-al developed in the nondirectional microphone 252 (R) of the directional control system, is delivered, after amplification in amplifier 262, to modulator 274, through condensers 280 and 281. This signal is impressed on the grids of modulator tubes 282 and 233 in phase. At the same time, a signal from oscillator 275 is impressed on the grids of modulator tubes 282 and 263, through the oscillator output potentiometer comprising resistances 283, 289, 290 `and 291, and the modulator input potentiometer comprising resistances 284, 28S, 236, and 287, which serve to adjust the proper relative levels of the 15,000 cycle signal and the oscillator signal. The oscillator signal is applied to the two grids degrees out of phase. As outlined in connection with FIGURE 1, the signal in the plate circuit of the modulator, which is similar in construction to the modulator of FIGURE 1, takes the form of la modulation envelope of the carrier suppressed type. It is well known, that a modulation envelope of this type created in a balanced modulator, when analyzed mathematically, will be found to contain, first, a signal having a frequency equal to the frequency of the signal applied 180 degrees out of phase to the grids of the two tubes; second a signal having a frequency equal to the sum of the frequencies of the `signal -applied in phase and the signal applied 180 degrees out of phase; `and third, a signal having a frequency equal to the difference of the two applied frequencies. For use with a control signal of 15,000 cycles l have selected a local oscillator frequency of 14,500 cycles, though it is understood that other frequencies may be used. The plate circuit of modulator 274 will therefore contain, under these conditions, a signal of 14,500 cycles frequency, a 29,500 cycle frequency, and la 500 cycle frequency. Both the primary and secondary windings of coupling transformer 292 are tuned to 500 cycles per second by means of condensers 293 and 294. The 29,500 cycle frequency and the 14,500 cycle frequency are therefore eliminated, and the signal impressed 180 degrees out of phase on the grids of demodulator 276, after passing through transformer 292, will consist of the 500 cycle frequency alone.

The oscillator signal, after passing through transformer 295, is now impressed in phase on the grids of tubes 2% and 297 in demodulator 276 which operates in the same manner as the modulator. The plate circuit of demodulator 276 will therefore contain a 500 cycle frequency, a 15,000 cycle frequency, and a 14,000 cycle frequency. Both windings of transformer 298 are, however, tuned'to 14,000 cycles by condensers 299 and 300, so that the output contains only the 14,000 cycle signal. This 14,000 cycle signal is impressed on potentiometer 260 which reduces the level of the signal in accordance with its setting and delivers it to the control grid of pentode tube 302 in voltage amplifier 277. Tube 302 amplities the signal and delivers it to the grid of triode tube 306, through coupling transformer 303, both windings of which are tuned, by means of condensers 304 `and 305, to 14,000 cycles for purposes of further attenuating any remnants of the 15,000 cycle`or 500 cycle signals which may have been impressed on the input of amplifier 277. Tube 306 in power amplifier 278 further amplifies the signal, provides power, and impresses the signal on loudspeaker 303, through output transformer 307.

Loudspeaker 308 therefore emits a 14,000 cycle neutralizing signal whenever the 15,000 signal emitted by the torpedo is picked up by the microphone system. For a given lsetting of potentiometer 260, the amplitude of the 14,000 cycle signal emitted by loudspeaker 308 is proportional to the `amplitude of the '15,000 cycle signal received. That is, if the torpedo is relatively close to the escort vessel, the amplitude of the 15,000 cycle signal received will atadas-i be high, and the loudspeaker will emit a loud 14,000 cycle signal. On the other hand if the torpedo is some distance away from the escort vessel, the 15,000 cycle signal received will be weak, and the 14,000 cycle signal emitted by the loudspeaker will be correspondingly weak.

It is necessary, however, not only to have the 14,000 cycle neutralizing signal proportional to the 15,000 cycle signal of the torpedo, as the two signals leave the hull of the escort vessel, but also so to control the amplitude of the neutralizing signal that the two signals will be actually equal in amplitude at the remote location of the torpedo. This matter is complicated by the fact that the amplitude of the 15,000 cycle signal emitted by the torpedo and reflected by the hull of the escort vessel back to the torpedo Varies at the location of the torpedo, depending on the azimuth of the torpedo with relation to the escort vessel. Thus, if the torpedo is abeam, a strong reflection will be received from the broad sides of the escort vessels hull. However, if the torpedo is ahead or astern, most of the 15,000 cycle sound wave will be reliected diagonally from the slanting hull of the escort vessel, and only a small part of the wave front will be reflected back from irregularities in the prow or stern of the escort vessel, to the torpedo. For a given distance of the torpedo, or in other words, for a given received amplitude of the 15,000 cycle signal, the amplitude of the 14,000 cycle neutralizing signal must vary with the azimuth of the torpedo, being large if the torpedo is abeam and small if the torpedo is ahead or astern, and of intermediate value if the torpedo lies between these positions.

lt is the function of potentiometer 260 to fulfill these conditions by adjusting the gain of the neutralizing system, and accordingly the amplitude of the emitted neutralizing signal. The setting of this potentiometer is controlled by the position of cam 258, which in turn is dependent on the azimuth of the torpedo. Cam 258 is shaped particularly to fit the reiection characteristics of the escort vessel and is attached to the motor shaft in such la way that its longest axis is generally in line with slider 259 when the torpedo is astern or ahead. Under these conditions, therefore, the slider is moved to the left, reducing the gain of the neutralizing system, and effecting the emission of a neutralizing signal of low amplitude. When the torpedo is abeam, the shaft rotates as the microphone :axis follows the soundwave front, bringing the cam into a position such that its shortest axis comes into line with slider 259. Slider 259 moves to the right under the inuence of spring 309, increasing the gain of the neutralizing system and effecting the emission of a neutralizing signal of high amplitude. Cam 25S is cut to the proper shape to cornpensate for any variations in the reflection coefficient of the escort vessels hull throughout the entire 360 degrees of azimuth, taking into account any irregularities in the hull, projecting fittings, etc. The neutralizing system therefore emits a neutralizing signal of amplitude such that at any point remote from the escort vessel the level of the neutralizing lsignal will be exactly equal to the level of the 15,000 cycle control signal reflected from the hull of the escort vessel. The two signals then act upon the control system in the torpedo in the manner described in connection with FIGURE 1 and FIGURE 2.

Oscillator 275, containing tubes 316 and 311, transformer 295, tuning condenser 313, and coupling condensers 314 and 315, is similar in construction to oscillator 24 of FIGURE 2, and need not be described in detail.

preferred to emplo` as the means for actuating the control system, a sound-wave signal, signals of other types may be used to actuate the control system in accordance with the mathematical theory outlined .hereafter under the heading Theoretical Consideration of the Control System. For example, a radio signal might `be employed, the microphone `system being in this case replaced by a directional antenna system, such as a pair of vertical antennae, or a loop antenna, and a non-directional antenna system such as -a single vertical antenna. Electro-magnetic radiation of relatively low frequency might also serve as the propagated control signal, inductance coils or loops, spaced in accordance with the mathematical theory, being used in place of the microphones.

T lzeoretical consideration 0f the control systemv A simplified schematic diagram of the microphone input circuits employed in both the control channel and the neutralizing channel is shown in FIGURE 4A. Referring first to the directional microphone system, consisting of microphones A and B and transformer 20, the Voltage delivered 'by this system to the input terminals of the high frequency microphone amplifier will be:

es=Nfi (1) Where:

es is the instantaneous voltage impressed on the grid.

N is the turns ratio of the transformer.

ep is the instantaneous voltage across the primary of the transformer.

In turn, since microphones A and B 'are connected 180 degrees out of phase:

Where eA is the instantaneous voltage generated by microphone A and eB is the instantaneous voltage generated `by microphone B.

Equation 2 Iassumes that the impedance presented to the microphones by the primary winding of the transformer is nearly infinite, and that therefore the entire voltage developed by the microphones is impressed on the transformer. This is a condition easily `approximated in practice.

Now, referring to FIGURE 4B, assume that a sound wave, two successive troughs of which are represented by lines PQ and RS, approaches the microphone system along a line CD. The direction of motion of the wave may be considered to be from C to D, and the wave front makes an angle, or, with the line joining the microphones. Assume that at any given moment the electrical signal generated by microphone R has a voltage:

6R=E cos 0 (3) Where E is the maximum amplitude of the signal, and 0 is the phase angle of the signal.

The phase angle of the sound wave may be 'also represented `by 9, :as demonstrated in the graph of FIGURE 4C, the vertical axis `of which represents the amplitude of the sound wave, and the horizontal axis of which represents its phase angle. In this ligure, zero phase angle is assumed to exist at the moment when microphone R, the location of which is indicated below the curve, is subject `to maximum amplitude of the sound wave; in other words the graph of the sound wave amplitude is a cosine curve. The sound wave is assumed to move from left to right across the page.

Then at any given moment, the voltages generated in microphones A and B, assuming their responses to be identical to microphone R, will be:

eAzE cos (04m) (4) and eB=E cos (l-u) (5) lnegative to positive.

Where u is the -angular phase difference existing in the wave between the two microphones, A and B, and the reference microphone, R.

Then returning to Equation 2,

Combining the two terms of Equation 6 in accordance with a well-known trigonometric identity:

epz-2E sin 0 sin u Now, referring to FIGURE 4B, the angular phase difference, u, in the wave between the locations of microphones A and R, and between B and R, may be seen For the expression (d/2+)\) represents the fraction of Now, the continuously varying phase angle, 0, is of course equal to:

Where f is the frequency of the signal and t is the time. Substituting (12) in (7), we obtain.

epz-ZE sin (2m-fr) sin u (13) And substituting (11) in (13), we obtain,

@,:aE sin (saft) sin (14) Then, returning to Equation 1, the voltage impressed on the grid of the microphone amplifier is seen to be:

WD Sin et) e.= -aNE sin (2me) sin Equation 15 reveals several important facts with regard to the variation of the input potential with rotation of the microphone system, or with variation in the direction of approach of the sound wave. in the first place, there is seen to be no variation in the difference of phase between the non-directional signal, as represented by Equation 3, and the directional signal, as represented by Equation 15, as the microphone system is rotated, except that, as the value of o: passes through Zero, the value of the last factor of Equation 15 changes from positive to negative, thereby changing the value of the function from In other words, the phase of the directional signal suddenly changes by 180 degrees as the value of a passes through Zero, when the front of the sound wave becomes parallel to the line joining the microphones. Aside from this change, the two signals always bear the same phase relationship to one another, through out the entire 36() degrees of rotation, the directional signal always remaining a sine function while the non-directional signal is a cosine function. Other phase reversals will occur if the value of D is sufficiently large as to make the ratio between D and the wave-length 1 or greater than 1. There is at no time, however, a gradual change in phase in the directional signal: all phase changes are in the nature of sudden reversals resulting in instantaneous phase displacements of exactly 18() degrees.

The maximum amplitude of es is, however, continuously dependent on the Value of a becoming greatest when the value of is such as to make the value of the angle in the second factor of Equation 15 an odd multiple of 9() degrees. 1f, for example, DzA/Z, Equation 15 becornes eSz-Z NE sin (Zyrft) sin (1r/2 sin a) and the maximum amplitude of es has maximum values at a:, 270, etc. when the axis of the microphone system points at the sound source. Regardless of the value of D, minimum values of es, maximums always occur at arzt) degrees, degrees, etc., when the wave front is parallel to the line joining the microphones, under which conditions the value of es is zero. If the ratio between D and the wavelength is greater than 1 other minirnal values will occur at other values of a.

Equation l5 can, of course, be converted to give the value of the maximum amplitude of es instead of the instantaneous value. This maximum value will always occur, during the time cycle, when sin (Zvfft) is l, since a sine function cannot exceed l in value.

rThen Es=2NE sin M =es maximum (16) ln FTGURE 4D values of ES and of sin u are plotted against a for four ditferent values of the ratio between D and the Wave-length. Examination of this figure shows that when D is less than one-half wave-length on increase in the separation, D, raises the maximum value of ES, but does not change the value of a at which this maximum value prevails, 90 degrees, 270 degrees, etc. When D reaches a value of one-half wave-length, however, the function reaches a maximum value of 2.0 NE, and this value cannot be exceeded, because the value of the sine factor in Equation 16 can never exceed 1. Further increases in D therefore result in the creation of secondary minima, as shown, which have their minimum values at 9() degrees, 27() degrees, etc. The maximum values of Es remain at a value of 2.0 NE, but are displaced along the axis, and there are two maxima instead of one. When D reaches a Value of one whole wave-length, the minima at 9i) degrees, 270 degrees, etc., have decreased to zero, and if D increases beyond one wave-length, the curve crosses over the zero axis and becomes negative. (This is not shown in EGURE 4D.)

As explained in connection with FIGURE 1 it is desirable to employ a signal frequency as high as possible, in order to assure the secrecy of the method used. As the frequency becomes greater, however, the wave-length decreases, increasing the value of D for a given separation in terms of wave-length. FIGURE 4C shows that the frequency cannot be increased to a point where D has a value of one wave-length, or a greater value, because such values result in zero values of ES at points other than 0 degrees, 18() degres, etc. FIGURE 4C also shows, however, that for values of D only slightly less than onehalf wavelength, such as D=.9 wave-length, although the secondary minima exist, the Value of ES remains negative during the first two quadrants of rotation from a=0 to o=180, `and positive throughout the second two quadrants, from a=180 to a=360. Values of D in excess of one-half wave-length, but less than one whole Wave-length, may, therefore be used, since the only requirement for successful functioning of the system is that ES shall be positive for one half of a full revolution and negative for the other half. As detailed in connection with FGURE 1, a value of D equal to .9 wave-length has been selected `for application in the practical embodiment of the control system.

It will now be convenient for purposes of reckoning to transform Equation 15 into the form of Equation 7, eliminating .the detailed expressions representing the two angles. Substituting back in Equation 15 the equivalent as of (21rft) developed in Equation 12 and the equivalent of (vrD Sil'l or) developed in Equation l1, Equation becomes:

This voltage is now applied to the grid of the micro* phone amplifier in the directional microphone system, is amplified by the amplifier and delivered to the modulator grids by the output transformer, through the series condensers in such a manner that the voltage appearing on the modulator grids has the same value and sign on the grids of both tubes. lf the voltage gain produced by the amplier, taking into account the circuit losses, be represented by k1 then the voltage applied to the modulator grids will be:

At the same time, a second alternating voltage generated by oscillator Zd is applied to the grids of the modulator in such a manner that the grid of one tube is always positive while `the grid of the other tube is negative, and vice versa. This Voltage may be represented as:

Where E,5 is the maximum amp'titude of the oscillator' voltage applied to the modulator grids, and fg, is the frequency of the oscillator.

The net instantaneous alternating vol-tage applied to the grids of the tubes accordingly has the following Values:

For ltubel e2: gt (21) Now lboth modulator tubes are operated on a portion of their characteristic near the cut-off point. If it be assumed that the characteristic curve in this neighborhood is parabolic in form, then vthe relationship between the plate current and grid voltage of either tube may be Written as follows:

(23 where Substituting in Equation 23 the values of grid voltage obtained for the two tubes in Equations and 21, we obtain, for the plate currents in the two tubes:

24 Since these currents flow in opposite directions through the output transformer they must be substracted, to obtain the value of the voltage in the secondary of the transformer. Completing this process of substraction, we obtain: (neglecting the direct current components, which will not pass through the transformer):

(26) Where:

ed is the instantaneous voltage impressed on the detector Ifrom the directional microphone system.

k3 is a constant determined by the relation of the output transformer characteristics to the constants of the circuit.

Substituting the original meanings of e0 and ew as defined in Equations 18 and 19, we obtain:

In Equation 27, the rst term represents the frequency of oscillator 24, and the second term represents the useful components of the modulated wave. The first term per- `forms no useful function in the circuit, and it is desirable to suppress it. This suppression is brought about, in the practical embodiment of the control system by the tuned input circuit of the diode detector, which responds only to the second term, and by keepin-g E, the amplitude of the control signal -muoh larger than Ew the amplitude of the oscillator signal. To all intents and purposes, therefore, the directional voltage actually impressed on the diode detector may be represented by:

and is seen to represent the effective voltage gain in the directional microphone channel between the microphone terminals and the diode detector input terminals.

Tlhe signal .of Equation 29 may ,be represented by a conventional modulation envelope of the carrier suppressed type. Such a modulation envelope is shown in FIGURE 4E (3). FIGURE 4 E also shows for reference purposes, in (.1), the incoming control signal generated by the directional microphone system, and, in (2), the low frequency signal of the oscillator, 24. In 4E (l) and 4E (3) `the solid line represents the Wave form obtained when sin u is negative, as under these conditions es is shown by Equation 15 to be positive. The positive sine function Ishown by the solid line of FIGURE ll-3(1) will therefore represent the incoming signal whenever the clockwise `angle of rotation of the sound-wave front is in excess of 18() degrees, or, what amounts to the same thing, whenever the angle of rotation, a, is counterclockwise, and less than degrees. The solid line of FIG- URE 4E(3) in turn represents the output of the modulator for a similar counterclockwise rotation of the sound- Wave front. The dotted lines in FIGURE 4E(1) and 4E(3), on the other hand, represent the result when sin u is positive, or, in other w-ords, when the sound-Wave front is rotated in a clockwise direction less .than 180 degrees. This distinction between the two sets of curves is indicated in the small diagram below FIGURE 4E, in which the arrow `represents the direction of approach of the sound wave.

The directional voltage represented by Equation 29 is now combined, in the diode detector input circuit, with the non-directional voltage derived from the reference microphone. This voitage, as originally generated by 25 the reference microphone, R, was given by Equation 3 as:

eR=E cos (30) ln the process of amplication in the non-directional microphone amplifier, this signal is reversed in polarity, so that it appears in the plate circuit as:

ep=k4E cos 9 `(31) The current ilowing in the plate circuit is given by:

D=ep ME cos 0 (32) This current flows through the inductance, and sets up a Voltage across it:

eL :jz'pXL: -jkiE (cos 6) D The (-j) in Equation 35 means that eL lags behind E cos 0 by 90 degrees. Or:

Maan, RD E S111 0 611:91.) lf the constant in the above expression be represented by Kn the equation becomes:

enzKnE sin 0 (36) The yresult of adding the directional signal ed and the nondirectional signal en in the diode input circuit is to create a signal:

:E sin 0(1'n-2Kd sin u sin qb) (37) This signal is a modulation envelope of the conventional 100 percent modulation type, although modulation does not, of course, reach l0() percent under all conditions. The shape of the envelope for the condition where sin u is negative-that is, Where the sound-wave front is rotated counterclockwise, less than 180 degreesis shown in FGURE 4e(5). It will be observed that in this case the outline or the modulation envelope is in phase with the original low frequency signal from oscillator 2d.

FIGURE 4E(6) shows the shape of this signal when lthe soundwave -front is rotated clockwise less than 180 degrees, producing a positive value of sin u. Under these conditions, the outline of the modulation envelope is 180 degrees `out of phase with the original low frequency signal from oscillator 24.

The diode detector now recti-es the signal of Equation 37. The end result of this process of rectication, assuming that ZKd sin u is not greater than Kn, and that modulation less than 100 percen-t is therefore maintained, is to elinn'nate the control `frequency sin 0 and the dire-ct current components of Kn, and to create a control signal:

ln this equation, the `amplitude of the control signal is shown to be dependent on a constant, KC, which has a value,

Where B is a constant depending on the shape of the diode :plate voltage-plate current curve, in the region used under the conditions of operation.

The frequency of 'the control signal is that of the local oscillator, and the amplitude is further seen to be dependent on `sin u, which in lturn is dependent -on the angle of 26 rotation of the sound wave front. As previously detailed, if the sound wave front is rotated less than degrees in a counterclockwise direction, sin u .is negative, and the control signal becomes: positive, or in other words, in phase with the original signal generated by oscillator 24.

On the other hand, if the sound wave front is rotated less than 180 degrees in a clockwise direction, sin u is positive, and the resulting value of the ec, the control signal, is negative: in other words, it is 180 degrees out of phase with the oscillator signal of Equation 19.

In either case, the amplitude of the control signal will depend on the absolute numerical value of sin u, which `follows the curve for D=.9 shown in FIG. 4D.

The control signal, after amplification, is now impressed on the tubes of the relay control tube system. The original signal of Equation 19 is also impressed on the relay control tube system. As detailed in connection with FIG- URE 2, if the signal impressed directly by the oscillator, e, is in phase with the signal derived from the modulator, ec, the control system is so constituted that the upper of the two tubes will break down, operating the upper relay, and turning the rudder in a clockwise direction. This condition will prevail when sin u is negative, or in other words when the sound wave front has been rotated in a counterclockwise direction, equivalent to a `clockwise rotation of the microphone system .and the aX-is of the torpedo. The clockwise Irotation of the -rudder will, theretore, bring the course of the torpedo back to bear on the source of the reilected sound wave.

lf, on the contrary, e is 180 degrees out of phase with eC the lower of the two tubes will break down, operating the lower relay, and turning the rudder in a counterclockwise direction. This condition will prevail when sin u is positive, or, in other words, when the sound wave front has been rotated in a clockwise direction, equivalent to a counterclockwise rotation of the microphonse system and the axis of the torpedo. The counter-clockwise rotation of the rudder in this case will, therefore, again bring the course of the torpedo to bear at the target.

The complete operation of the relay control tube system is illustrated in FIGURE 4F. The left hand section of this ligure, entitled sin u negative (counterclockwise rotation of sound-wave front) shows the condition when the control signal is in phase with the original oscillator signal. Under these conditions, the control signal impressed in phase on both tubes, as illustrated in curveV (l), is seen to be in phase with the oscillator signal impressed on tube 158, as shown in curve (2), but out of phase with the oscillator signal impressed on tube 159, as shown in curve (3). Tube 15S therefore tires, during the first half-cycle only when both elements of the tube are positive, but tube 159 does not fire, because during the entire cycle the two elements of the tube maintain opposite polarity.

On the other hand, if sin u is positive, as a result of a clockwise rotation of the sound-wave front, the condition will be as illustrated lin the right-hand section of FIG- URE 4F. Here it is seen that the control signal of curve (l) is in phase with the oscillator signal impressed on tube 15d, but out of phase with the oscillator signal impressed on tube 15S. Tube l5@ therefore tires, under these conditions, during the second half-cycle only. Tube 158, however, does not lire.

Theoretical consideration ofthe neutralizing system It is the object of the neutralizing system to create a neutralizing signal, EN, having an amplitude at a distance from the escort vessel equal to the amplitude at that point of the `control signal emitted by the torpedo and reilected from the hull of the escort vessel. If the amplitude of the reiiected control signal be designated as Er, then Where E1 i-s the amplitude cf the incident control signal, before reflection, KA is the attenuation constant to the point considered, and Kr is the coefficient of reflection of Vthe escort vessels hull a-t the particular point where the reflection talces place: and

In the neutralizing system, the incident signal E1 is picked up and impressed on the modulator. As demonstrated in Equation 26 the output of the modulator will be of the form where K1 is a constant dependent on the circuit characteristics and the gain in the amplifier and modulator stages, e is the local oscillator voltage and the other constants have the meaning assigned to them in connection with Equation 26.

If, now,

eozEo Sin and e=E1 sin (21rf1t) (44) where E0 and E1 are the maximum amplitudes of the oscillator signal and the incident signal respectively, and fo and f1 represent their respective frequencies, then (42) becomes em=K1(a1E0 sin (2m-fot) -l-ZQZEO sin (2n-fit) E0 sin (zwfof) (45) Equation 45, when resolved by ordinarily trigonometric methods becomes The output of the modulator is thus seen to contain three frequencies; the frequency of the local oscillator, a frequency equal to the difference between the frequencies of the incident signal and the local oscillator, and a frequency equal to the sum of the two impressed frequencies. The filter action of the tuned windings of the modulator output transformer eliminates the first and third terms, and impresses only the second term on the demodulator input. The effective modulator output may therefore be represented as m=KMEi Sin @Mfr-fom (47) The action of the demodulator is identical with the action of the modulator, except that in this case, the local oscillator is applied to both grids in phase, and its frequency must, therefore, be treated analytically in the same manner as fi in the modulator. The effective output of the demodulator, after elimination of the unwanted frequencies will therefore be For the frequencies adopted for practical application, f0=14,500 cycles, and f1=15,000 cycles, the output of the demodulator has a frequency of (2X 14,500- 15,000) cycles, or 14,000 cycles.

This signal is amplified and applied to the loudspeaker, which emits a signal, the amplitude of which, at a distance from the escort vessel is QNIKNKAEi Sin (2a(2f0-fr) f) 50) where KN is an overall constant representing the conversion factors of the conversion from sound wave to electrical wave form, and vice versa, the effective gain of the electronic circuits, etc. It is seen that Equation 50 is of the form set up in Equation 41 as the funda- 5; mental requirement of the neutralizing system. To fullfill the requirements completely, however, it is necessary that It is the function of the directional control system to bring about this equality. This control system automatically adjusts the gain of the neutralizing system so that it is at all times equal to the coefficient of reflection, at Whatever point of the escort vessels hull the reflection takes place.

The amplitude of the signal of Equation 5() is, therefore which is the relationship desired.

From the preceding mathematical proofs, it will be apparent that within the scope of my control system signals, all other types than sound-wave may be utilized for actuating the system. For example, radio signals or electro-magnetic radiation of low frequency might serve as the control signal in place of sound-waves.

Where hereafter in the appended claims the term friendly vessel appears, it is used in broad sense to indicate the vessel from which the torpedo was launched, convoys or other friendly vessels near the location of the torpedo or any stationary object which it is desired to protect from injury by the torpedo.

I claim:

1. An automatic control system for marine torpedoes, comprising a directional microphone system and a nondirectional microphone system combining in response to a sound signal proceeding from the target, to produce an electrical signal the phase and amplitude of which is dependent on the direction of approach of said sound signal, an electronic control system for converting said electrical signal into a control signal having related phase and amplitude characteristics, and an electro-magnetic rudder control system responsive to the phase and amplitude characteristics of said control signal for operating the rudders of said torpedo reversibly.

2. An automatic control system for marine torpedoes comprising, means for directing a sound signal against a target to cause reflection of said signal therefrom, a directional microphone system and a non-directional microphone system combining in response to a refiected signal to produce an electrical signal possessing characteristics dependent on the direction of approach of said sound signal, an electronic control system for converting said electrical signal into a control signal having characteristics dependent on the direction of approach of said sound signal, and a rudder control system responsive to said directional characteristics of said control signal, for operating the rudders of said torpedo reversibly.

3. An automatic control system for torpedoes comprising apparatus for generating and broadcasting a sound signal, an electro-magnetic rudder control system in the torpedo, a directional microphone system and an nondirectional microphone system in the torpedo combining to receive the refiection of said signal from a target and to generate, in combination with a modulator system, an oscillator system and a detector system, a control signal possessing characteristics dependent on the direction of approach of said sound signal, a relay control tube system in the torpedo responsive to said characteristics of said control signal to actuate said rudder control system and to direct the torpedo at the target, and an interrupter for alternately disabling said microphone systems and said apparatus for generating said broadcasting a sound signal.

4. A control system for automatically directing a torpedo at the target in response to a sound signal reflected from the target, comprising in the torpedo a signal generator and loudspeakers for generating and broadcasting a sound signal, a directional microphone system responsive to the reflection of said sound signal from the target,

amasar a non-directional microphone system responsive to the reilection of said sound signal from the target, a low trequency oscillator, a modulator for combining the output of said oscillator with the output of said directional microphone system, a detector for combining the output of said modulator with the output or" said non-directional microphone system, and for rectitying the resulting signal to produce a control signal having characteristics dependent on the direction of approach of said sound signal, a relay control tube system for operating control relays selectively in accordance with said characteristics of said control signal, an electro-magnetic rudder control system responsive to the operation of said relays, a rudder or controlling the direction of said torpedo under the control of said rudder control system, and an interrupter for alternately disabling said microphone systems and said signal generator.

5. A control system for torpedoes, comprising a signal generator and loudspeakers for generating and broadcasting a sound signal, a directional microphone system f responsive to the reflection of said sound signal from the target, a nondirectional microphone system responsive to the reflection of said sound signal from the target, a low frequency oscillator, a modulator for combining the output of said oscillator with the output of said directional microphone system, a detector for combining the output of said modulator with the output of said nondirectional microphone system, and for rectifying the resulting signal to produce a control signal having phase characteristics dependent on the direction of approach of said sound signal, a relay control tube system for operating control relays selectively in accordance with CII said phase characteristics of said control signal, and electro-magnetic rudder control system responsive to the operation of said relays, a rudder for controlling the direction of said torpedo under the control of said rudder control system, to direct the torpedo at the target, an interrupter for alternately disabling for a predetermined interval of time said microphone systems and said signal generator', a similar control system, a modulator system, a demodulator system, an amplifier system, and a loudspeaker system located at the position of an object other than the target, combining to receive said sound signal to convert it to a neutralizing signal of similar amplitude but of dilerent frequency, and to broadcast said neutralizing signal from said object, and a neutralizing control system in the torpedo for receiving said neutralizing signal and applying it after conversion to said relay control tube system to neutralize the eiects of the reliection of said sound signal from said object other than the target.

Reiter-ences Cited hy the Examiner UNITED STATES PATENTS 2,109,475 3/38 Fanning 114-23 2,166,991 7 39 Guanella 340-6 2,262,931 11/41 Guanella 340-16 2,282,402 5/ 42 Hefele 340-16 2,349,370 5/44 Orner 340-16 2,396,463 3/46 Hammond 114-21 2,422,446 6/4-7 Stuart 340-16 BENlAMiN A. BORCHELT, Primary Examiner.

FRED C. MATTERN, IR., Examiner. 

1. AN AUTOMATIC CONTROL SYSTEM FOR MARINE TORPEDOES, COMPRISING A DIRECTIONAL MICROPHONE SYSTEM AND A NONDIRECTIONAL MICROPHONE SYSTEM COMBINING IN RESPONSE TO A SOUND SIGNAL PROCEEDING FROM THE TARGET, TO PRODUCE AN ELECTRICAL SIGNAL THE PHASE AND AMPLITUDE OF WHICH IS DEPENDENT ON THE DIRECTION OF APPROACH OF SAID SOUND SIGNAL, AN ELECTRONIC CONTROL SYSTEM FOR CONVERTING SAID ELECTRICAL SIGNAL INTO A CONTROL SIGNAL HAVING RELATED PHASE AND AMPLITUDE CHARACTERISTICS, AND AN ELECTRO-MAGNETIC RUDDER CONTROL SYSTEM RESPONSIVE TO THE PHASE AND AMPLITUDE CHARACTERISTICS OF SAID CONTROL SIGNAL FOR OPERATING THE RUDDERS OF SAID TORPEDO REVERSIBLY. 